The Apex Predator
by TheMadKatter13
Summary: A demon shouldn't have fingers so gentle. AU: alpha!KnightOfHell!Cas / omega!angel!Dean.


**The Apex Predator**

**by TheMadKatter13**

**SUMMARY~A demon shouldn't have fingers so gentle. AU: alpha!KnightOfHell!Cas / omega!angel!Dean.**

**DISCLAIMER~The rights to Supernatural reside with the WB and the CW and Eric Kripke (and probably a lot of other people that I'm too lazy to look up) and I receive no financial gain from the writing of this story.**

**AN~Inspired by the wonderful AU, demon!Cas, I first found on tumblr on 'thewinchesterlifestyle'. I am in love with this trope, someone send help. The story title is taken from the Otep song of the same name (well, 'Apex Predator') which was my personal soundtrack while writing this.**

**The Apex Predator**

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"I must say this is unexpected." The blue-eyed, brown-haired demon was staring at him curiously from across the small room, head tilted to the side in puzzlement and posture lax. No, not just _a_ demon-a Knight of Hell. Dean's wings raised in a blatant, threatening gesture.

"It's not really any of your business, is it asshole?" he snapped back. It wasn't hard to figure out what the Knight was talking about. Sure, it was rare to find a soldier angel who was an omega rather than an alpha, but it was near unheard of to find one, _in_ battle, in heat. And Dean was. Both an omega and in heat. Well, almost in heat. But still in battle. And cornered. Overall, not a scenario any angel would like to find themselves in. But Dean had always been rather good at getting himself into situations that seemed hopeless. Not on purpose, it just happened. He always got himself out though. Him, or one of his garrison would be right behind him, slaughtering anything in their way to get to him. He doubted anyone would be coming today though. It was a massive battle, and nearly everyone had been separated before he'd even started chasing demons down these halls.

"It could be my business," the demon replied, lips quirking. The Knight's power was subtly increasing, pushing on his grace, trying to pressure him into accepting the strong alpha in front of him. His wings fluttered, wanting to lower in submission, in enticement, for a potential mate, one who would clearly provide him with strong, healthy offspring. The demon took a step forward and his wings snapped back up, his race's instincts overriding his secondgender's. At least, for the moment. The demon raised his hands, a human gesture of placation, though the tilt to his lips was a strong indicator that it was done quite sarcastically, as he stepped back, his power receding with him.

"You wish!" Dean growled, raising his angel blade. Fuck but he really wanted to be mounted, and now. He had plenty of partners to chose from who would have no problem fucking him without mating him. But they were either home in Heaven or down here, fighting their own battles. The demon was still standing between him and his only exit. He gritted his teeth and shifted his weight, preparing to run-fly at the demon, to knock him off balance and barrel past. The Knight didn't move though, even though his movements would have been screaming his intentions loud and clear. He just kept standing there, posture loose, oddly non-threatening, and that same mocking tilt to the corners of his lips.

"I have forever," the demon said, gravelly voice light, eyes glittering with amusement. Dean calculated the chances he could kill the thing on his way out. Were he not tipping into his heat right now, the answer would be: fairly good. As it was, slick was already beginning to drip and his grip on his blade was growing weak as his body demanded he drop and present. He could feel his fingers trembling with the effort it took to keep it in his hand and the thought of dropping it honestly terrified him.

"Which will end when I put my blade through your chest," he threatened, baring his teeth and raising his wings even further, his feathers rustling lightly as they puffed out, increasing his threatening display. A tremor of need wracked his spine and a groan escaped where he was trying to hold it in at the top of his chest, his eyelids fluttering.

"You won't do that," the Knight said, voice confident. So confident that Dean raised an eyebrow.

"Not for lack of effort," he snorted under his breath, readjusting his grip. All right, he had two options here: the offensive one (trying his luck getting past the Knight) or the defensive one (stay in the corner and make sure no one occupied it with him until his heat passed or until one of his fellow angels came for him). He eyed the patient smirk on the Knight. No way in Hell (pun very much intended, thank you) was he going to stay here and risk getting killed, or worse, mounted, while in his heat.

He moved immediately, not giving his decision time to show on his face or in his posture. He shot towards the Knight, seeing them widen in surprise as he dropped his wings like he was entering a dive, in order to increase his speed. His collision with the other vessel caused it to go flying, crashing into the rocks of the cave. The angel didn't bother making sure his opponent was truly down before he was off again, flying out the tunnel as fast as he possibly could. Other tunnels and rooms passed him by as he tried searching for the one that would take him back to the main battle, to the other angels, to safety. As he flew, his heat just kept increasing until he knew he was pumping out pheromones at maximum capacity.

A wave of power washed over him, either stronger than he'd ever felt or just appearing so because of the weakness his heats always brought, and his wings stuttered, sending him crashing into a wall. He stumbled from the rubble created by the crash, wings fluttering, trying to straighten out his feathers by will alone, their disarray setting his nerves even further on edge. Even stronger was the unease caused by not knowing who had hit him though the power felt vaguely familiar. Another wave hit him so hard that he dropped to his hands and knees, his body desperately trying to get back breath it didn't really need.

"Fuck," he gasped, tremors of need wracking his whole body, tingling up his arms and down his legs. "Fucking shit fuck."

"What a filthy for an angel." That same, attractive, gravelly voice as before reached his ears shortly before the wave of power did. The omega in him was _screaming_ to be mounted, not used to being denied for this long.

"Fuck off," Dean spat, nearly all of his concentration aimed at his violently trembling arms, both of which wanted to give way to allow for his ass to be shoved into the air, even though his back was to the wall. There were faint sounds of approaching steps from farther up the tunnel and he knew it was that same Knight who'd caught up to him.

"Mmm. Your strength is really to be commended, lasting against me as long as you have in the condition you're in." He could hear the demon's footsteps grow closer and with a burst of strength fueled solely by adrenaline, he shoved up, sitting back on his heels in a move that was for comfort as much as it was for being one of the few positions that was self-sustaining. The demon was just a few paces away from him now, much closer than he'd been in the cave but he his vessel was just as handsome and pristine as when the demon first found him. Waves of power were pressing on his grace again, coming from all sides, trying to coerce his wings down into a more submissive position. Most odd of all was that the power wasn't forceful like the grace of alphas back in heaven. It was firm, but not forceful, almost gentle, and his wings fluttered in response of such kindness, wanting to lower, wanting to submit.

"Why are you doing this?" Dean gasped, fighting his own body in trying to get his wings to return to and stay in a threatening pose. "Why not just kill me already? We both know I can't fight back like this." They rose, trembling, but only so far as to drape against the wall at his back, unable to hold themselves up any longer. Fuck, he _wanted_.

"Because I want a mate." His eyes widened in surprise and he stared up at the demon with a feeling akin to dread. Or rather, that's how he wanted to look up at the Knight because in any other circumstance, that's how he'd feel. But right now, right on the cusp of his heat, the arousal running rampant in his system was _all he could feel_.

"Why me? Why not a demon?" He was baiting the demon by asking, but he had to know. He needed answers. He needed mounting. His wings twitched, aching to drop, to submit. It took everything in him to not give in. His cock and his ass though, he had no control over the way his cock was hard and aching, no control over the way his ass dripped with slick. No control for the oil dripping from his wings either. He barely had any energy left to remain upright as it was.

"I have never wanted a demon mate. Distrustful, deceitful things." The Knight smiled as if it were a joke. And the omega supposed if he could really be paying attention right now, even he'd see it as that. "You, though. Strong thing, aren't you? An omega soldier. Coming down here right when your heat is about to start. And I know how strong I am. But still you resist me." Resistance that wouldn't last much longer. Dean had come into contact of demons of all sorts, even his fair share of Knights, but this one... None of them were ever this calm, this gentle about their powers or their pheromones. Why was this one different? What trick was it playing?

Another wave of need swept through him and he tipped backwards, back slamming into the wall. He couldn't raise his arms any more, he felt so weak. He couldn't move his legs or even bring his chin up from where it had fallen against his chest. He needed mounting and he needed it right fucking now. Why had he thought he could fight this battle and be back in time for someone to service his heat? Stupid stupid stupid! Steps drew closer, slow, even. His blade was just sitting in his hand, loose and just four fingers away from falling to the dirt. He didn't want to be in this place when he was so vulnerable; a high keening sound slipped from between his lips like a whistle, quite uninvited.

"Shhh... No need for that," the Knight said as he dropped to a crouch in front of him. Firm, gentle hands cupped his face and raised it so that he could meet those deep blue eyes. The demon's pheromones were washing over him, soaking him in them. He felt another wave of slick from his holes and on his wings and he whimpered. "I'll take care of you, pretty thing." Dean didn't even have the power to shake his head. Any second now, he would be flopping to the ground, doing whatever it took to raise his arse into the air for this demon to take him. A demon who was slowly getting more and more attractive to him. The omega in him recognized the source of power, and what a power it was. Stronger than most of his brothers- and sisters-in-arms. Mating with this demon would be like mating with an archangel. He keened highly again as his head started to swim with base desire. Suddenly, arms were around and under him and the world was shifting, making him so dizzy he couldn't figure out what was up and what was down.

"Let's get you somewhere where we won't be bothered," he heard the demon saying but the sound came from far away, words muffled, and next all he knew was darkness.

When Dean awoke, it was clothesless and face down on a soft bed, his heat in full swing and and fingers in his feathers.

Now, even in heaven, other angels just _couldn't_ seem to get the procedure right for him. He'd seen other alphas with other omegas, even the alphas that had serviced him in the past servicing other omegas, preening them with their fingers, and the omegas went wild from it. But whenever an alpha attempted to preen him, it always felt _wrong_. Like they were going opposite the grain even when they clearly weren't. It drove Dean crazy. But the fingers in his feathers now, preening him and spreading the mating oils along each tawny one, were perfect; firm and gentle. The by-now familiar power surrounding his grace was the same. He didn't know it could even feel like this and he moaned, slowly drawing his knees under him and sticking his ass up in the air.

"Alpha, please," he whispered, hoping those finger would never stop. Stroking an angels wings was the erotic equivalent as a human's cock being stroked.

"I'm pleased to see you're awake," came the familiar gravelly voice of the Knight. He was past caring about race though, the basest part of his mind only knowing that there was a strong alpha there to take care of his heat and that it knew how to treat him how he wanted to be treated. "I was beginning to worry I would have to start without you."

The fingers left his wings and he tensed, letting out a frantic sound of despair. They were back immediately, the Knight shushing him easily, stroking through his feathers until he was as relaxed as when he'd woken up, slumped and pliant. Power teased along the edges of his hole, encouraging the slick to fall even faster and he whined, desperate to be filled. He wanted to fuck himself backwards on that feeling but power and grace didn't work that way.

"Fuck me," he begged. "Please fuck me, knot me." His knees spread and he shuffled his front forward to further expose his hole, just more enticement to the alpha to where it needed to be.

"I wonder what our eggs will look like, our fledglings when they hatch..." he could hear being mused from behind him.

"Beautiful," he gasped. "Strong. _Please._" The ache was filling him, the emptiness, until it was all he knew. It _hurt_.

"Yes, they will be. Now shhh... I'll take care of you. I will always take care of my mate." Had Dean been more conscious of himself than he was now, he would have heard those words and realized what they meant. As it was now, he was too far gone for the words to do anything other than turn him on and attract him to the alpha. The power teasing him withdrew and then an alpha cock was replacing it before he could complain.

Just the tip of it was thick, comforting. It pressed forward, easily aided by the slick he was producing. He should have been prepared beforehand, but the stetch of being entered wasn't painful in this state, it was delicious, comforting him even that there was an alpha mounting him. There was a low moan sliding from between his lips; encouragement, it was all encouragement. The fingers on his wings were still stroking through his feathers, methodically he realized now. They had started from the top and were slowly working their way down, coating his wings in his slick from base to tip. They were still firm, still gentle.

"You are...incredibly tight, my angel," the demon murmured as it bottomed out inside him. He had never felt so _full_. "You feel as if you've never been mounted before." Somehow, those words sunk into his mind and something about them prompted him to respond.

"I have," he managed to reply. "I always have someone to take care of my heats. I would have had someone if I'd managed to get home before my heat started."

The demon snarled and pulled out sharply, only to slam back in, striking the spot inside him roughly in such a way that pleasure burst in white sparks behind his eyes.

"I will be the only one to take care of your heats from now on," the Knight snarled, pulling out and thrusting back in just as roughly. "I do not share." His pace was rough, animalistic, _fulfilling_. Alpha angels were always careful, concerned they could hurt what they considered their weaker counterparts. Not this alpha. He _knew_ what Dean needed and seemed more than happy to give it to him. The alpha's cock was filling that emptiness inside of him, better than any angel before had, wiping their memories from his mind with each stroke. The Knight's fingers had reached the bottom of his wings and they felt drenched with his mating oils. A pressure was building up inside him, the one that would give temporary reliefe from the heat that wracked his body with such annoying needs.

"Yes alpha, please take care of me. Please." He knew the alpha would. There was no doubt to his intentions of keeping the omega sated until his heat passed. But still, he felt drawn to respond, to beg. That's what heats did to omegas: turned them into writhing, begging messes.

"Always." The Knight draped himself along his back, hands moving from preening his feathers to gripping the tops of his wings near the bases, the most solid point of contact. His thrusts were growing, if possible, even more animalistic and rough and the omega dropped his forehead to the soft pillow below him, baring the back of his neck. His instinctual side wanted this strong mate of which he had no doubt would take care of him and any hatchlings borne of their coupling.

The pleasure was spiraling higher and higher, like how he would in a mating dance, and he knew that soon it would reach its apex and send him spiralling back down in the most spectacular fashion. The knot at the base of the alpha's cock was growing, bumping against his rim and making the thrusts that much shorter as the alpha continued to dominate him ruthlessly. And he was loving every second.

"Knot me! Knot me knot knot me knot me!" he cried, feeling his release approaching at terrifying speeds. With a growl and an exceedingly hard thrust, the knot popped in and he cried out as it pressed everywhere it needed to to fulfill him. So close so close so close he just needed... There was a snarl and then teeth were embedding in the back of his neck, marking him, power wrapping around and threading through his grace, binding him to his mate, irrevocably. The knot in him ballooned, filling him even more, better, and it was all too much. Dean came with a cry, cock untouched and passage rippling around his alpha's cock, a chain reaction that had the demon spilling into him, the semen hot, so hot.

The teeth in the back of his neck slowly released before a tongue lapped at the marks, power seeping into the holes that each tooth had made in his skin until he felt so full of his alpha's cock and his come and his power that he couldn't tell up from down or right from wrong. He was reduced to a panting mess on the bed, weak and powerless, at the mercy of the alpha on whose cock he was impaled. As he lay there though, his heat receded in it's temporary fashion and consciousness came back to him. And it came to him exactly _what_ he had allowed to mount him breed him mark him mate him, just as he felt another flood of warmth caused by his mate's ejaculation.

Dean went stiff under the body of the demon, every muscle tesning best as it could in its weakend state. The hands gripping his wings released and he whined despite himsef, and the next thing he knew, those firm gentle fingers he could remmeber from his heat and before were stroking through his feathers again, preening the limp wings which were draped on either side of him in a way that could convey both utter exhausteion and complete submission. If those fingers kept up what they were doing, he was going to be hard before the next round of his heat even hit. As it was, all tension drained immediately from him at the attentino of his alpha. The knot keeping them together deflated and he groaned as the alpha cock slipped from him. Hands curled around his knees, pulling them out from underneath him until he was laying flat on his belly. The belly that would soon be swollen with his new mate's eggs. He had no idea how to feel about that.

"I think it may be a good idea to know your name, my mate," the Knight said from above him, a warm weight settling over his hips as the fingers began to preen him in earnest.

He let out a low, contented moan, his exhale ending with a breathy "Dean." On one hand, he was mated to a demon, a Knight of Hell. Which meant that should anyone kill his mate, as any angel worth his salt would likely attempt to do should they encounter the demon, then Dean would die too. What would the council do about it? Him? Them? Would they sacrifice one angel for the sake of getting rid of a Knight of Hell? Would breaking the bond like that even kill a Knight? Not much was known about them currently. They were still new, creations of Lucifer and trained by Cain himself. He had fought several, but in each altercation, he'd only been able to wound them (and them, him).

Then there was the other side of things. The side where no alpha angel had ever fucked him as thoroughly in an entire heat as this demon had in one round. And his fingers. By his father, no demon should have fingers that gentle. It went against nearly everything that they were. But the demon did have them. His fingers were more gentle than any other who'd ever touched his wings, and just as firm. How had he even known how to treat him? Had he had an angel before? How did he know what Dean needed?

"Am I your first?" Somehow, that came out as the most important of questions.

"First fuck?" the demon chuckled and, in the intamacy of the moment, it seemed particularly cruel. "No, pretty thing. No you are not. First angel though? Yes, you are. And the last." Despite himself, as this entire encounter really had been, the words flooded his heart with warmth, with comfort.

"What is your name?" It took him a bit, but he finally realized that this Knight was not one he recognized, had never fought before.

"Castiel." Dean's eyes rose and he almost choked on nothing.

"_You're_ Castiel?" The Knight was said to be one of the strongest in all of Hell. How the fuck had he attracted such a mate?!

"Yes, Dean." Those fingers were still combing through his feathers, and he would have been hard pressed to say they weren't making sure to attend to each individual feather. So thorough, so unnaturally kind for a demon. He didn't know what to do. Accept his new mate or fight with every bit of him there was?

A new wave of arousal and need swept through him, announcing the next round of his heat. His cock swelled between his body and the bed and he moaned, rotating his hips. The fingers in his wings stilled and he could hear his new mate take a deep breath, could hear him inhaling the pheromones he was starting to exude anew.

"Fuck, Cas," he groaned, gyrating his hips, grinding his cock against the bed for some much-needed friction.

"I intend to," came the Knight's amused voice as Dean was picked up. He groaned, wanting to resist the change in position but hardly able to do anything about it. He was turned and his mate was propping himself up against the wall at the head of the bed, pulling Dean back down onto his cock. He couldn't take his eyes from his new mate's and the way the blue glittered at him. "I'm going to fuck you full of hatchlings, Dean. So many to fill our nest. Strong, beautiful hatchlings."

A hand slid to rest on his stomach, right where he would start to swell as the hips below him bucked hard, making him jump into the air only to fall right back down on the thick cock that seemed to be reaching even deeper inside him than it had before and he moaned, unable to stop loving, stop needing, the way it filled him so completely. Cas's hips continued to buck under him, thrusting him into the air and letting his body impale itself. All he could do was wrap his arms around his alpha's neck and stare helplessly into those stupid blue eyes that only seemed to get bluer the longer he stared, sucking him in thrust by thrust. He realized then that he was stuck here, with this mate. He didn't want to die, couldn't let his mate die, the father of thier children. He couldn't allow it. He wouldn't allow it.

"Fuck."

FIN

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**I didn't even get a paragraph into this story before I knew it was going to have a sequel. I'm not sure what it's called yet or when it will come out, but it will feature Cas!POV, worried!Cas, and pregnant!Dean (no birthing). But if you're interested in that, don't forget to follow my tumblr author page, 'TheMadKatter13-fanfiction', which will keep you updated.**


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